carbon dioxide

American  

[kahr-buhn dahy-ok-sahyd] / ˈkɑr bən daɪˈɒk saɪd /

noun

1. a colorless, odorless, incombustible gas, CO 2 , present in the atmosphere and formed during respiration, usually obtained from coal, coke, or natural gas by combustion, from carbohydrates by fermentation, by reaction of acid with limestone or other carbonates, or naturally from springs: used extensively in industry as dry ice, or carbon dioxide snow, in carbonated beverages, fire extinguishers, etc.

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carbon dioxide British  

noun

1. Also called: carbonic-acid gas. a colourless odourless incombustible gas present in the atmosphere and formed during respiration, the decomposition and combustion of organic compounds, and in the reaction of acids with carbonates: used in carbonated drinks, fire extinguishers, and as dry ice for refrigeration. Formula: CO 2

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carbon dioxide Scientific  

1. A colorless, odorless gas that is present in the atmosphere and is formed when any fuel containing carbon is burned. It is breathed out of an animal's lungs during respiration, is produced by the decay of organic matter, and is used by plants in photosynthesis. Carbon dioxide is also used in refrigeration, fire extinguishers, and carbonated drinks. Chemical formula: CO ₂ .

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carbon dioxide Cultural  

1. A compound made up of molecules containing one carbon atom and two oxygen atoms.

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Discover More

Carbon dioxide is normally found as a gas that is breathed out by animals and absorbed by green plants. The plants, in turn, return oxygen to the atmosphere. (See carbon cycle and respiration.)

Carbon dioxide is also given off in the burning of fossil fuels (see greenhouse effect).

Etymology

Origin of carbon dioxide

First recorded in 1870–75

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Compare meaning

How does carbon-dioxide compare to similar and commonly confused words? Explore the most common comparisons:

• carbon monoxide vs. carbon dioxide

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Example Sentences

See Examples For:

carbon dioxide

Annual emissions in 1990 were about 431 million metric tons of carbon dioxide equivalent.

From Los Angeles Times ● Oct. 22, 2026

"So what are the residents actually breathing in? It's not fresh oxygen; it's carbon dioxide and pollutants. And what happens as a result? The body – specifically the brain – doesn't get enough oxygen."

From BBC ● Oct. 20, 2026

Eventually plants trapped so much carbon dioxide, which is necessary for photosynthesis, that CO2 levels in the atmosphere plummeted by 90%.

From The Wall Street Journal ● Oct. 16, 2026

The broader computational framework may also prove useful well beyond carbon dioxide hydrogenation.

From Science Daily ● Oct. 14, 2026

Its air is thin, containing mostly carbon dioxide but also some molecular nitrogen and argon and very small quantities of water vapor, oxygen and ozone.

From "Cosmos" by Carl Sagan

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